Cyclophosphamide (CY) can augment cell-mediated immunity, including tumor-directed immunity, in experimental animals. Immunopotentiation is probably due to killing or functional impairment of suppressor T cells. Administration of 1,000 mg of CY per square meter 3 days before a sensitizing dose of keyhole limpet hemocyanin (KLH) significantly augments the acquisition of delayed-type hypersensitivity (DTH) to KLH in patients with advanced carcinoma. We will determine whether pretreatment of such patients with lower doses of CY (300 mg per square meter) augments DTH to KLH and dinitrochlorobenzene (DNCB), and the antibody response to KLH. Furthermore, we will determine the cellular basis for the augmentation of immunity by studying the composition and function of blood mononuclear cells at various times after administration of CY. Composition will include enumeration of total T cells and the helper-inducer and suppressor-cytotoxic subsets by staining with fluorescinated monoclonal antibodies and analyzing with the cell sorter. Function will include responses to mitogens and allogeneic cells, and pokeweed mitogen-driven antibody production. Also, we will study the proliferative response of lymphocytes to KLH and DNCB-conjugated autologous mononuclear cells to determine whether these responses correlate with DTH, are augmented by incubation with activated CY and are specifically suppressed by T cells, or soluble factors made by T cells, from unresponsive patients. Finally, we will determine the effect of CY on tumor-directed immunity by vaccinating melanoma patients with autologous, irradiated melanoma cells mixed with BCG, either 3 days after CY pretreatment or without CY. We will compare the DTH responses of the CY and control groups to autologous tumor cells in vivo and the lymphoproliferative and lymphocytotoxic responses to autologous tumor cells in vitro.